1. Field of the Invention
This invention relates to an electromagnetically driven valve control system for internal combustion engines, and more particularly to an electromagnetically driven valve control system of this kind, which controls intake valves and/or exhaust valves of the engine, which are electromagnetically driven.
2. Prior Art
A basic construction of an internal combustion engine having intake valves and/or exhaust valves of a electromagnetically driven type is disclosed by U.S. Pat. No. 3,882,833, in which the intake and/or exhaust valves are driven by springs and solenoids. Further, a control system for an internal combustion engine of this kind which employs the above basic construction is conventionally known, for example, from Japanese Laid-Open Patent Publication (Kokai) No. 2-112606, which is capable of changing the output timing of driving signals supplied to valve-driving solenoids according to the rotational speed of the engine.
Still further, an electromagnetically driven valve for use in the above basic construction has also been proposed, for example, by U.S. Pat. No. 5,222,714, which has an electromagnetic driving mechanism thereof improved such that an electromagnetic force required of the solenoid is reduced to the minimum.
However, none of the above proposed techniques contemplate the states of the intake valves and exhaust valves just before the start of the engine. As a result, there is a fear that if the intake valves and/or exhaust valves remain open when the engine starts to be cranked, the valves can collide with the pistons within the combustion chambers of the engine, and in the worst case intake valves, exhaust valves and/or engine components such as pistons can be broken or damaged. Besides, a disconnection in the wiring for supplying driving signals to the valves or the like causes the electromagnetic driving mechanism to fail. However, no electromagnetically driven valve control system has been proposed yet which has a function of detecting such a disconnection or the like.
In addition, none of the above proposed techniques contemplate the relationship between the timing of the stopping of the supply of electric power to the solenoids of the intake valves and exhaust valves and the positions of the respective pistons within the combustion chambers at the time of turning-off of the ignition switch of the engine. As a result, for example, the supply of electric power to the solenoids can be stopped before the engine is completely stopped and consequently intake valves and/or exhaust valves can unfavorably collide with pistons within combustion chambers, which can lead to breakage of the valves and/or engine components.